Electron-sensitive photographic plate



June 25, 1957 H. B. I Aw ET AL 2,797,331

ELECTRON-SENSITIVE PHOTOGRAPHI C PLATE Filed March 18, 1952 GLA 55 PLATEafcmaf United States Patent Oiiice 2,797,331 Patented June 25, 1957ELEcTRoN-SENSITIVE PHoroGRAPHIC PLATE Application March 18, 1952, SerialNo. 277,132 1s Claims. (cl. 25o-49.5)

This invention relates, in general, to electron-sensitive photographicplates and, more particularly, to plates which are capable of recordingelectron images but which are relatively insensitive to ordinary visiblelight.

It has been found desirable to have some method of photographing imagesproduced by electron optical systems where. the electrons are generatedby a thermionic emitter. This problem arises, for example, in plottingthe positions at which phosphor dots are to be deposited on the viewingscreen of one type of tri-color televisin kinescope tube. One methodutilized for plotting the positions of the dots is to expose aphotographic plate, through an electron-focusing grid of crossed wires,to a thermionically generated beam of electrons scanned across the areaof the plate. The grid of wires has aperturesto permit: passage of theelectron beam wherever it is desired to place a phosphor 'dot on thecompleted screen. After the photographic plate has been properly exposedto the electron beam to form a multiplicity of latent dot images, theplate is developed and a print is then made on a medium which is to beused for actual printing of the phosphor dots on a base member. Thismethod of plotting is more fully described and claimed in a copendingapplication of Harold B. Law, Serial No. 277,133, filed concurrentlyherewith and now Patent 2,727,828.

In developing the above described process, it was found that ordinarytypes of photographic plates are not suitable,for at least two reasons.One reason is that a Athermonic emitter generates visible light. Anordinary photographic plate is exposed immediately by the light andrendered useless to record electron optical images. Another reason isthat an ordinary photographic plate is a good electrical insulator and,when exposed to an electron beam, accumulates an electrical charge whichhas an undesirable effect on the characteristics of the electron opticallens system which is used to plot the position of the phosphor dots. Itwas, therefore, found necessary to devise a photographic plate whichwas, initially, at least, sensitive to record electron optical imagesbut relatively insensitive to visible light and was, at the same time, afairly good electrical conductor.

One object of the present invention is to provide a photographic platewhich is sensitive to electrons, electrically conductive, and relativelyinsensitive to ordinary visible light of predetermined wavelengths.

Another object of the invention is to provide a photographic plate whichis sensitive to electrons but relatively insensitive to the lightgenerated by a thermionic emitter.

Another object of the invention is to provide anv improved photographicplate for recording images formed in electron optical systems.

Still another object of the invention is to provide an improved electronsensitive photographic plate which can be used in an electron opticalsystem without having any undesirable effects on the lenscharacteristics of the system.

These and other objects will be more apparent and the invention will bemore readily understood from the following detail description and theillustrative drawing of which:

Fig. 1 is a perspective view of one embodiment of a photographic plateconstructed in accordance with the principles of the present invention;and

Fig. 2 is a cross-section view taken through the line II--II of Fig. l.

In general, the present invention comprises an improved photographicplate and methods of making the improved plate. The plate comprises abase member having disposed on a surface thereof a layer of conventionalphotographic material which is also electron sensitive. The photographicmaterial is covered with an electrically conducting coating and is alsoprovided with a light filtering substance capable of filtering out mostof the light in the visible wavelengths to which the photographicmaterial is sensitive. For particular purposes, the exposed surface ofthe photographic material may be provided with an electrode.

A preferred example of method of preparation of a preferred embodimentof a photographic plate in accordance with the principles of the presentinvention will now be given.

The improved type of photographic plate of the present invention may bemade by modifying a conventional plate comprising a transparent glassbase member having one surface coated with a gelatin emulsion containingsilver halide salts, for example, silver bromide and silver iodide.Plates of the kind which are suitable are sold under the trade. nameKodalith In the first step of the modication process, the surface of thegelatin emulsion is treated, in the dark, by wetting it with an aqueoussuspension of graphite (Aquadag). This suspension may be prepared bymixing` the graphite and water in the proportion of about l gm. of theformer per cc. of the latter. This proportion is not at all critical,however, and any other convenient proportions may be selected from whicha thin, even coating of the graphite can be deposited. In the wettingprocess, the suspension is briskly agitated to obtain an evendistribution. Excess suspension is poured off the surface of the plateand the plate is permitted to drain. This provides a very thin,lighttransmitting coating of graphite on the surface of the emulsion.This coating has a very high electrical resistance.

The second step of the process is to impregnate the gelatin emulsionwith a red organic dye. This may be done by making. up a saturatedaqueous solution of Basic Fuchsin dye (.335 gm./liter) and soaking thegraphite coated plate in the solution for about 5 minutes. The surfaceof the plate is then rinsed and dried.

Next, the graphite-coated surface of the plate is rendered moreconducting by gently polishing or burnishing with a piece of softmaterial, such as absorbent cotton. The burnishing action apparentlycauses the graphite particles to overlap and touch each other at asufficient number of points to lower the electrical resistance of thesurface to a considerable extent.

The plate which is made as described above is cornplete so far as someapplications are concerned. However, if the plate is to be used torecord dot-images in the process of manufacturing certain types oftri-color television kinescope tube viewing screens, it is necessary tomaintain it at a particular potential. In order to do this, an electrodeshould be applied to the coated surface ofthe plate. This may be done bypainting an air-drying silver paste in the form of a stripe around theedges of the coated surface.. The paste may comprise, for example, acolloidalI suspension of`silver in anr organic medium including avolatile organic solvent. The organic medium may be, for example,nitrocellulose in amyl acetate.

A plate, as made by the above described example of the process of thepresent invention, is shown in the drawings'. In the figures, a glassplate 2 carries on one of its surfaces a layer 4 of gelatin emulsioncontaining silver halide salts. The emulsion is impregnated with a reddye and has its outer surface 8, which is the one opposite the glassplate 2, covered with an electrically conducting coating of graphite 10.This coating is just thick enough to be a fairly good electricalconductor but is not thick enough to prevent passage of light. When heldup to the light (after the plate is developed), the appearance of thegraphite coating is that of lightly smoked glass. Its surfaceresistivity should preferably be from l to l negohms. The completedplate which is illustrated also includes a silver paste electrode 12 inthe form of a stripe around the edges of the coated surface 8.

A method of utilizing the photographic plate which has been describedabove is described and claimed in vthe previously mentioned copendingapplication of Harold B. Law. As explained in the copending application,the plate may be exposed to an electron beam which is generated by athermionic emitter such as a glowing wire filament. The filament givesoff visible light within a broad range of wavelengths in the visibleportion of the' spectrum. Ordinary photographic emulsion, such as thatdescribed herein, are relatively insensitive to light in the red regionof the visible spectrum but are sensitive to light in the other regions.In the present case, however, the red dye filters out nearly all of thelightin the visible wavelengths, except the red rays, and thus rendersthe photographic emulsion relatively insensitive to all visiblewavelengths to which it would otherwise be sensitive. In the case of thepreferred example described, sensitivity of the plate was reduced toabout one-hundredth its normal value.

Exposure of the photographic plate to a focused electron beam from thethermionic emitter produces a latent image wherever the beam strikes theemulsion. The plate is later developed in conventional manner to bringout a visible image. This may be printed on any conventionalphotographic printing medium by exposing to an ordinary incandescenelamp. The exposure is somewhat longer than usual since much of the reddye is still present in the plate after developing and washing.

Complete insensitivity to light of most visible wavelengths is notdesired in this case since printing registration marks are put on theplate by exposure to light rather t `scope of the invention. The basemember may be some transparent medium other than glass, for example,mical or synthetic resins. Also, the base member need not be transparentif printing of the image is done by reected light. In this case, themember may be a metal, such as aluminum, or metal coated with enamel. v

The photosensitive emulsion may be any one of hundreds of conventionalcompositions. Although gelatin containing silver halide salts ispreferred to obtain good contrast, the material may comprise merelybichromated gelatin, or gelatin with cerium salts. Also, the suspendingmedium may be collodion (nitrocellulose) or other film forming materialsin which light-sensitive materials can be incorporated. The particularphotosensitive material used is not critical.

'I'he particular substance used to render the `photographic plateinsensitive to ordinary visible light depends partially on thecomposition of the photosensitive material utilized. Since mostphotosensitive materials are usually sensitive to all wavelengths in thevisible portion of the spectrum except red, the light ltering substanceshould usually be a red organic dye. Many different red organic dyes maybe used, for example, Eosin, Neutral Red, Saffi-onine, Rose Bengal, andAlizarin Red S. Any red organic dye can be used which does not have anunfavorable reaction with the photosensitive coating material. If it isdesired to use a light sensitive material which is insensitive towavelengths other than red, some other colored dye can be used.

The light filtering material need not be impregnated in the photographicemulsion. It may be applied as a surface coating only, for example. Thisis more desirable if the photographic material is a suspension incollodion rather than gelatin.

The eleirically conductive coating also does not have to be graphite. Itmay, for example, be a thin, light transmitting coating of a metal suchas aluminum applied by evaporation in vacuo. If applied in this manner,the heating filament must, of course, be shielded from the photographicplate in such a manner-than no light from the filament reaches theplate.

What is claimed is:

l. A photographic plate comprising a base member having on a surfacethereof a layer of electron-sensitive photographic material, said layerhaving on at least the surface opposite said member a stratum of lightfiltering material comprising an organic dye capable of preventing thepassage of substantially all light of predetermined wavelengths in thevisible portion of the spectrum, said filtering material beingsubstantially transparent to the passage of electrons, and also having astratum of light' transmitting electrically conducting material.

2. A plate according to claim l in which said base member is lighttransmitting.

3. A plate according to claim 1 in which said photo graphic material isa gelatin emulsion containing a photosensitive material.

4. A plate according to claim 3 in which said gelatin emulsion containsa silver halide salt.

5. A plate according to claim 1 in which said dye is a red dye.

6. A plate according to claim 5 in which said dye is Basic Fuchsin.

7. A plate according to claim l in which said electrically conductingmaterial is carbon.

8. A photographic plate comprising a glass plate having on a surfacethereof a layer of photographic emulsion, said emulsion havingsutiicient red organic dye impregnated therein to exclude substantiallyall visible light in the blue and green portions of the spectrum andhaving on the surface thereof an electrically conducting,lighttransmitting coating of graphite.

i 9. A plate accordingto claim 8 in which said red dye is Basic Fuchsin.

l0. A method of making a photographic plate comprising applying to asurface of a plate a layer of electronsensitive photographic material,applying to the surface of said photographic material a stratum ofelectrically conducting, light-transmitting materiaL'and impregnating atleast part of said layer of photographic material with an organic dyecapable of filtering out substantially all visible light of all of thewavelengths to which said photographic material is sensitive.

1l. A method according to claim 10 in which said electron-sensitivephotographic material is a gelatin emulsion containing a silver halidesalt.

l2. A method according to claim ll in which said elecl tricallyconducting material is graphite.

13. A method according to claim l2 lin which said graphite is applied tothe surface of said emulsion in the form of a water suspension, theplate is then dried and the surface is burnished in order to decreasethe electrical resistance thereof.

14. A method according to claim 13 in which said dye is applied to thegraphite coated surface of said plate in the form of a Water solution,before said polishing step.

15. A method according to claim 14 in which said dye is a red dye.

16. A method of rendering a photographic plate suit able for recordingimages in an electron optical system where the electron source is athermionic emitter, comprising applying an electrically conducting,light-transmitting coating to the sensitive surface of said plate andtreating the photosensitive material of said plate with a lightfiltering organic dye capable of filtering out substantially all visiblelight of all wavelengths to which said photosensitive material issensitive.

17. A photographic plate comprising a base member having on a surfacethereof a layer of electron-sensitive photographic material, said layerhaving on at least the surface opposite said member a stratum of lightltering material comprising an organic dye capable of preventing thepassage of substantially all visible light of predetermined wavelengths,said plate `:also including at least a surface stratum of electricallyconducting, light-transmitting material, and an electrode making goodelectrical Contact with a portion of said electrically conductingmaterial.

18. A plate according to claim 17 in which said electrode is a coatingof metallic paste adjacent the edges of said electrically conductingmaterial.

References Cited in the tile of this patent UNITED STATES PATENTS816,172 Morse et al. Mar. 27, 1906 1,973,886 Scanlan et al. Sept. 18,1934 2,372,170 Baker Mar. 27, 1945 2,446,248 Schrader Aug. 3, 19482,542,304 Boucher Feb. 20, 1951

1. A PHOTOGRAPHIC PLATE COMPRISING A BASE MEMBER HAVING ON A SURFACE THEREOF A LAYER OF ELECTRON-SENSITIVE PHOTOGRAPHIC MATERIAL, SAID LAYER HAVING ON AT LEAST THE SURFACE OPPOSITE SAID MEMBER A STRATUM OF LIGHT OF FILTERING MATERIAL COMPRISING AN ORGANIC DYE CAPABLE OF PREVENTING THE PASSAGE OF SUBSTANTIALLY ALL LIGHT OF PREDETERMINED WAVELENGTHS IN THE VISIBLE PORTION OF THE SPECTRUM, SAID FILTERING MATERIAL BEING SUBSTANTIALLY TRANSPARENT TO THE PASSAGE OF ELECTRONS, AND ALSO HAVING A STRATUM OF LIGHTTRANSMITTING ELECTRICALLY CONDUCTING MATERIAL. 